"Thank you Sir for the clarity between obsolescence & seasonal."
Obsolescence, obsolete, obsolescent are very nuanced terms, and can be confusing, especialy when used in a left-handed sort of way that the ammo industry can approach the process.
Obsolete is the easiest to understand, and lines up nicely with "out of production." the .41 Rimfire is a good example of an obsolete cartridge. Guns haven't been manufactured for it for decades, and other than a few special runs, neither have cartridges.
Obsolescent/Obsolescence means that the cartridge is dying out. There are a lot of cartridges that are obsolecent, yet they're still manufactured. This is most analagous to cartridges that are classed seasonal production. Generally, guns for obsolescent cartridges are no longer manufactured but are readily available, which means the cartridge can remain in a state of obsolescent for literally decades while also remaining perfectly financially viable.
.300 Savage, .250 Savage, .32 S&W, .38 S&W (and so many more) have been surpassed by other chamberings and are slowly losing the popularity they once had, but people still want the ammo to supply the many guns that are still out there.
One of the neatest aspects of our sport is that a cartridge that's been obsolete for literally decades, with no firearms or ammo production, can spring back to life.
The biggest generator of the "old is new again" phenemon (sp?) has been, in my opinion, Cowboy Action Shooting.
.41 Short and Long Colt, .38 Long Colt, .44 Colt, .44 Russian, .45 Schofield, are all cartridges that were obsolete, but which are now seeing at least limited production, all to meet the needs of the CAAS people.
Hell, there have even been some new guns chambered in .44 Russian and .45 Schofield in the past decade or so, which is astounding considering that neither one of them survived in new guns in the production upheaval caused by World War I